The present invention relates to a method and a composition for the determination of a compound having mercapto group (hereinafter referred to as SH compound).
With regard to the determination of SH compound, the following methods have so far been known: (1) titration method using organomercury compound such as p-chloromercury benzoic acid, (2) colorimetric method using sodium nitroprusside and (3) colorimetric method using Ellman's reagents such as 5,5'-dithio-bis(2-nitrobenzoic acid) (hereinafter referred to as DTNB).
These methods have the following disadvantages. Method (1) uses organomercury compound, and is much susceptible to influences of living body components in a sample, when applied to clinical inspections, owing to the measurement in the ultraviolet region. In method (2), colored reaction solution is unstable to change of temperature, and wavelength for measurement is low. In method (3), wavelength for measurement is low.
Thus, development of a method for the determination of SH compound with higher accuracy has been desired. As a result of studies to this end, it has been found that a pigment formed by reaction of a compound represented by the general formula (I), as will be described later, with SH compound has a maximum absorption wavelength of about 600 nm and has distinguished characteristics such as less susceptibility to influences of components in a sample, particularly living body components; possible measurement in the visible region; good sensitivity; possible determination of a small amount of a sample; good solubility in water.